Different component portions of, for example, gas turbine blades require different types and thicknesses of protective coatings, and some portions require that there be no coating thereon since, otherwise, the strength of the component is dramatically reduced. The application of the different types and thicknesses of protective coatings in some regions, and the prevention of coating deposition in other regions, while using the most efficient coating techniques, can pose difficult problems for those components which are newly manufactured or repaired, and may have existing coatings thereon and/or may need new coatings applied. In many cases, it is difficult to achieve the desired combination of protective coatings and uncoated surfaces.
Furthermore, due to high local mechanical loads, airfoils may be coated only in sub-regions where the limited extensibility of the erosion-protection coating does not present any mechanical risk. Therefore, a local masking device is needed which is to be adapted to the particular airfoil. The increasing complexity of 3D airfoil design and the difficult accessibility encountered in blisks increase the complexity required of the masks. In particular, the tolerances defined for airfoil coatings are often very narrow. Not only must the layer thicknesses be correct, but the coatings may be applied only where permitted.
Such a masking device is disclosed, for example, in DE 10 2008 053 394 A. A masking plate is disposed around the component to be processed. A gap is present between the component and the masking plate. Disposed in the gap is a felt or a brush seal that adapts to the contour of the component without damaging it.